[Intel-gfx] [PATCH 2/2] drm/i915/userptr: fix size calculation

[Chris Wilson]

Quoting Matthew Auld (2020-01-16 19:28:09)
> If we create a rather large userptr object(e.g 1ULL << 32) we might
> shift past the type-width of num_pages: (int)num_pages << PAGE_SHIFT,
> resulting in a totally bogus sg_table, which fortunately will eventually
> manifest as:
> 
> gen8_ppgtt_insert_huge:463 GEM_BUG_ON(iter->sg->length < page_size)
> kernel BUG at drivers/gpu/drm/i915/gt/gen8_ppgtt.c:463!
> 
> Fixes: 5cc9ed4b9a7a ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 3 ++-
>  drivers/gpu/drm/i915/gt/gen8_ppgtt.c        | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> index fef96a303d9d..81fa53495c9d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> @@ -405,6 +405,7 @@ static struct sg_table *
>  __i915_gem_userptr_alloc_pages(struct drm_i915_gem_object *obj,
>                                struct page **pvec, int num_pages)

Well that answers that question. Why not use unsigned long?

That's what the comment is all about, fixing the code! Not continuing to
bodge it.
-Chris